Base generator

ABSTRACT

The present invention provides a base generator having the structure of formula (1): 
                         
wherein R 1 , R 2 , R 3 , R 4 , R 5 , and Y {circle around (−)}  are defined as in the specification. The base generator of the present invention can be used for imidization of a polyimide precursor, promoting crosslinking of epoxy monomers, or crosslinking of polyurethane or polyurea.

FIELD OF THE INVENTION

The present invention relates to a base generator, and particularly to abase generator which exhibits good storage stability, can generate abase by exposure to heating or irradiation of light, and can be used forimidization of a polyimide precursor, promoting crosslinking of epoxymonomers, or crosslinking of polyurethane or polyurea.

BACKGROUND OF THE INVENTION

Polyimide is the first choice among high performance polymer materialsbecause of its excellent thermostability and desirable mechanical,electrical and chemical properties. Moreover, as requirements onsemiconductor performance have become increasingly rigorous, practicallimitations and deficiencies of conventional inorganic materials havegrown more pronounced. These limitations and deficiencies can be offsetin certain aspects by the properties of polyimide. Thus, the developmentof aromatic polyimide by Du Pont Corporation has attracted extensiveattention, resulting in development of a variety of polyimides withmultiple uses.

In the semiconductor industry, polyimides have been widely used inpassive film, stress buffer film, α-particle masking film, dry etchingmask, micro-electromechanical systems, interlayer insulating film, etc.;other new applications are continually being developed. Protectivecoating for integrated circuit devices is a predominant application,since polyimide materials have passed reliability testing for integratedcircuit devices. However, polyimide is not only applied in theintegrated circuit industry, but is also a key material in electronicpackaging, enameled wire, printed circuit boards, sensing elements,separation film and construction materials.

Typically, polyimide is synthesized by two-stage polymerizationcondensation. In the first stage, a diamine monomer is dissolved in apolar, aprotic solvent such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethyl formamide (DMF) or dimethyl sulfoxide (DMSO),and then an equimolar dianhydride monomer is added to the solution,followed by condensation at low temperature or room temperature, to formpolyimide precursor, i.e., polyamic acid (PAA).

In the second stage, dehydration-condensation and cyclization reactionsare carried out by thermal imidization or chemical imidization toconvert polyamic acid into polyimide. To obtain a polyimide polymer withexcellent electrical and physical properties typically requires heatingfor several hours at a high temperature of 300 to 400° C. in thermalimidization to form the highly imidized polymer. However, due totemperature restrictions inherent to some semiconductor processes,greater attention is gradually being paid to materials that can inducepolyamic acid be imidized at a low temperature.

In some applications, addition of a base will promote crosslinking ofmonomers to cure them into a polymer. However, direct addition of thebase to a formulation composition would give rise to disadvantages suchas reduced storage stability. Therefore, a technique has been developedto delay the effect of the base by providing a base generator in which abase is protected by a protecting group and will be generated after thebase generator is exposed to heating or irradiation of light.

Amines are commonly added as the base to catalyze low-temperatureimidization. However such amine compounds are likely to catalyzeimidization at room temperature. Mitsuru Ueda et al. developed a seriesof alkylamine thermal base generators (TBGs), as disclosed in ChemistryLetters, Vol. 34, p. 1372-1373 (2005); JP 2007056196A and Journal ofPhotopolymer Science and Technology, Vol. 21, No. 1, p. 125-130 (2008).Although the alkylamine thermal base generators can be used to catalyzeimidization, the polyimide polymer film obtained therefrom suffersinferior thermal and mechanical properties.

The present invention represents the culmination of research anddevelopment on the problems mentioned above. The inventors of thepresent invention found a novel base generator which can be used inimidization for the preparation of polyimide and is effective inlowering the cyclization temperature of polyimide and improving thethermal and mechanical properties of the polyimide polymer, so as tomeet demands in the industry.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a novel basegenerator, which can generate a base upon heating or irradiation oflight. The thermal base generator or optical base generator according tothe present invention can be used for imidization of polyimideprecursor, promoting crosslinking of epoxy monomers, or crosslinking ofpolyurethane or polyurea.

Another objective of the present invention is to provide a polyimideprecursor composition, which comprises a polyimide precursor and theabove base generator and is capable of forming polyimide by lowtemperature imidization.

Yet another objective of the present invention is to provide a methodfor preparing polyimide, which comprises polymerization of the abovepolyimide precursor composition by low temperature imidization.

Still another objective of the present invention is to provide apolyimide which is prepared by polymerization of the above polyimideprecursor composition by low temperature imidization and has excellentthermal and mechanical properties.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood from the detaileddescription given below, which is for illustration only, and thus is notlimitative of the present invention, and wherein:

FIG. 1 is a flow chart for testing the physical properties according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Herein, the term “alkyl” refers to saturated hydrocarbon groups,examples thereof including, but not limited to, methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl and the like.The term “aryl” refers to aromatic ring systems of 6-carbon monocyclicring, 10-carbon bicyclic ring or 14-carbon tricyclic ring, examplesthereof including, but not limited to, phenyl, tolyl, naphthyl,fluorenyl, anthryl, phenanthryl and the like. The term “haloalkyl”refers to alkyl substituted with halogen, wherein “halogen” meansfluorine, chlorine, bromine or iodine, preferably fluorine or chlorine.The term “alkoxy” refers to alkyl attached to oxygen atom, examplesthereof including, but not limited to, methoxy, ethoxy, propoxy,isopropoxy, n-butoxy, isobutoxy, pentyloxy, hexyloxy, benzyloxy,fluorenylmethoxy and the like.

The base generator according to the present invention has the structureof formula (1):

whereinR₁ and R₂ are the same or different and are each independently H, linearor branched C₁-C₆ alkyl, linear or branched C₁-C₆ haloalkyl, or linearor branched C₁-C₆ alkyl substituted with one or more C₆-C₁₄ aryl,

whereinR₆ is linear or branched C₁-C₆ alkyl, linear or branched C₁-C₆haloalkyl, linear or branched C₁-C₈ alkoxy unsubstituted or substitutedwith one or more C₆-C₁₄ aryl, or —NR₁₀R₁₁, andR₂, R₈, R₉, R₁₀ and R₁₁ are the same or different, and are eachindependently H, linear or branched C₁-C₁₄ alkyl unsubstituted orsubstituted with one or more C₆-C₁₄ aryl, or C₆-C₁₄ aryl;R₃, R₄ and R₅ are the same or different, and are each independently H,linear or branched C₁-C₆ alkyl unsubstituted or substituted with one ormore C₆-C₁₄ aryl, linear or branched C₁-C₆ hydroxyalkyl, linear orbranched C₁-C₆ cyanoalkyl, or C₆-C₁₄ aryl; andY^({circle around (−)}) is an anionic group.

According to an embodiment of the present invention, the groups R₁ andR₂ in formula (1) are the same or different and are each independentlylinear or branched C₁-C₆ alkyl,

whereinR₆ is linear or branched C₁-C₆ alkyl, linear or branched C₁-C₆haloalkyl, linear or branched C₁-C₈ alkoxy unsubstituted or substitutedwith one or more C₆-C₁₄ aryl, or —NR₁₀R₁₁; and R₇, R₈, R₉, R₁₀ and R₁₁are the same or different and are each independent H, linear or branchedC₁-C₁₄ alkyl, or C₆-C₁₄ aryl. Preferably, R₆ is methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl,trifluoromethyl, pentafluoethyl, methoxy, ethoxy, propoxy, butoxy,pentyloxy, hexyloxy, benzyloxy and fluorenylmethoxy; and R₇, R₈, R₉, R₁₀and R₁₁ are each independently H, methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, phenyl,benzyl or diphenyl methyl.

According to an embodiment of the present invention, the groups R₁ andR₂ in formula (1) are the same or different and are each independentlymethyl, ethyl, propyl, butyl or selected from a group consisting of:

Preferably, R₁ and R₂ are the same or different and are eachindependently methyl, ethyl or selected from a group consisting of:

According to an embodiment of the present invention, R₃, R₄ and R₅ informula (1) are the same or different and are each independently H,methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl,pentyl, hexyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl,hydroxypentyl, hydroxyhexyl, cyanomethyl, cyanoethyl, cyanopropyl,cyanobutyl, cyanopentyl, cyanohexyl, phenyl, benzyl or diphenylmethyl;preferably, hydroxybutyl is selected from a group consisting of

preferably, hydroxypentyl is selected from a group consisting of

preferably, cyanobutyl is selected from a group consisting of

and preferably, cyanopentyl is selected from a group consisting of

Preferably, R₃, R₄ and R₅ are the same or different and are eachindependently H, methyl, ethyl, n-propyl or isopropyl.

The anionic group in formula (1) is not particularly limited, examplesthereof including, but not limited to, halide ion, sulfate, nitrate,phosphate, sulfonate, carbonate, tetrafluoborate, borate, chlorate,iodate, hexafluorophosphate, perchlorate, trifluoromethanesulfonate,trifluoroacetate, acetate, tert-butylcarbonate, (CF₃SO₂)₂N⁻ ortert-butyloxy. According to an embodiment of the present invention, theanionic group in formula (1) is halide ion or tetrafluoborate.Preferably, the halide ion is fluoride ion and chloride ion.

The base generator according to the present invention can be prepared byany methods known in the art. For example, it may be prepared bydissolving an imidazole compound in a solvent under nitrogen, andreacting with anhydrides, isocyanates, alkylhalides, aromatics, sulfonicacids, acyl chlorides or phosphoric acids, followed by purification toobtain the base generator of the present invention.

The base generator according to the present invention can be used as anoptical base generator or thermal base generator, preferably a thermalbase generator which can be used for preparing polyimide by lowtemperature imidization, promoting crosslinking of epoxy monomers, orcrosslinking of polyurethane or polyurea. In the present invention, thelow temperature imidization is carried out at a temperature of nothigher than 250° C., preferably not higher than 200° C.

The present invention also provides a polyimide precursor compositioncomprising (a) a polyimide precursor and (b) the base generator havingthe structure of formula (1).

In the precursor composition according to the present invention, thepolyimide precursor is not particularly limited, and includes thosewhich can be readily selected by persons skilled in the art. Preferably,the polyimide precursor is selected from a group consisting of:

wherein,G and G₁ are the same or different and are each independently atetravalent organic group;each P independently represents a divalent organic group;each R independently represents linear or branched C₁-C₁₄ alkyl, C₆-C₁₄aryl, C₆-C₁₄ aralkyl, a phenolic group or an ethylenically unsaturatedgroup;each R_(x) independently represents H or an ethylenically unsaturatedgroup;each D independently represents a nitrogen-containing heterocyclic groupor a OR* group, wherein R* is linear or branched C₁-C₂₀ alkyl;each m is an integer from 0 to 100; andeach n is an integer greater than 0.

In the precursor composition according to the present invention, aweight ratio of component (a) to component (b) ranges from 2000:1 to5:1, preferably 1000:1 to 10:1, and more preferably 200:1 to 10:1.

According to an embodiment of the present invention, the ethylenicallyunsaturated group is not particularly limited, examples thereofincluding, but not limited to, ethenyl, propenyl, methylpropenyl,n-butenyl, isobutenyl, ethenylphenyl, propenylphenyl, propenyloxymethyl,propenyloxyethyl, propenyloxypropyl, propenyloxybutyl,propenyloxypentyl, propenyloxyhexyl, methylpropenyloxymethyl,methylpropenyloxyethyl, methylpropenyloxypropyl, methylpropenyloxybutyl,methylpropenyloxypentyl, methylpropenyloxyhexyl, a group of thefollowing formula (7) and a group of the following formula (8):

wherein R₁₂ is a phenylene, linear or branched C₁-C₈ alkylene, linear orbranched C₂-C₈ alkenylene, C₃-C₈ cycloalkylene, or linear or branchedC₁-C₈ hydroxylalkylene; and R₁₃ is hydrogen or linear or branched C₁-C₄alkyl. Among others, the preferred group of formula (8) is selected froma group consisting of:

According to an embodiment of the present invention, the tetravalentorganic groups G and G₁ are not particularly limited, examples thereofincluding, but not limited to, tetravalent aromatic groups ortetravalent aliphatic groups. The aromatic groups can be monocyclic orpolycyclic rings, preferably selected from a group consisting of:

wherein X is each independently hydrogen, halogen, linear or branchedC₁-C₄ perfluoroalkyl or linear or branched C₁-C₄ alkyl, and A and B areeach independently a covalent bond, linear or branched C₁-C₄ alkyl,linear or branched C₁-C₄ perfluoroalkyl; alkoxy, silanyl, oxygen,sulfur, carbonyl, carboxylate, sulfonyl, phenyl, biphenyl, or

wherein J is —O—, —SO₂—, —CH₂—, C(CF₃)₂ or C(CH₃)₂.

More preferably, the tetravalent organic groups G and G₁ are eachindependently selected from a group consisting of:

wherein Z is hydrogen or halogen.

Most preferably, the tetravalent organic groups G and G₁ are eachindependently:

According to an embodiment of the present invention, the tetravalentaliphatic groups are selected from a group consisting of:

According to an embodiment of the present invention, the divalentorganic group P is not particularly limited, such as, but not limitedto, an aromatic group. Preferably, the divalent organic group P is eachindependently selected from a group consisting of:

wherein,R₁₇ is each independently H, C₁-C₄ alkyl, C₁-C₄ perfluoroalkyl, methoxy,ethoxy, halogen, OH, COOH, NH₂ or SH;each a is independently an integer of 0 to 4;each b is independently an integer of 0 to 4; andR₁₈ is a covalent bond or a group selected from:

wherein,c and d are each independently an integer from 0 to 20;R₁₇ and a are as defined above; andR₁₉ is —S(O)₂—, —C(O)—, a covalent bond or linear or branched C₁-C₁₈alkyl.More preferably, each divalent organic group P is independently selectedfrom a group consisting of:

whereineach of a is independently an integer of 0 to 4; andeach Z is independently hydrogen, methyl, trifluoromethyl or halogen.

Most preferably, each divalent organic group P is independently

The divalent organic group P can also be a non-aromatic group, forexample, but not limited to:

wherein each R₂₀ is independently H, methyl or ethyl; ande and f are each independently an integer greater than 0.

Preferably, the 2-valent organic group P is

In the polyimide precursors of formulae (2) to (5), each R isindependently linear or branched C₁-C₁₄ alkyl, C₆-C₁₄ aryl, C₆-C₁₄aralkyl, a phenolic group or an ethylenically unsaturated group. Thelinear or branched C₁-C₁₄ alkyl is exemplified by, but not limited to,the following groups:

wherein p is an integer from 0 to 10. For example, the linear orbranched C₁-C₁₄ alkyl may be methyl, ethyl, n-propyl, isopropyl,1-methylpropyl, 2-methylpropyl, n-butyl, isobutyl, tert-butyl,1-methylbutyl, 2-methylbutyl, pentyl, hexyl, heptyl or octyl. Theethylenically unsaturated group is as defined above. The C₆-C₁₄ aryl orC₆-C₁₄ aralkyl mentioned above is preferably selected from a groupconsisting of:

R is most preferably selected from a group consisting of:

In the polyimide precursors of formulae (2) and (4), each R_(x) isindependently H or an ethylenically unsaturated group, wherein theethylenically unsaturated group is as defined above. According to thepresent invention, preferably each of the group R_(x) is independentlyH, 2-hydroxypropyl methacrylate, ethyl methacrylate, ethyl acrylate,propenyl, methylpropenyl, n-butenyl or isobutenyl, more preferably H or2-hydroxypropyl methacrylate of formula below:

In the polyimide precursors of formula (5), the group D is eachindependently an nitrogen-containing heterocyclic group or anOR*-containing group, wherein R* is linear or branched C₁-C₂₀ alkyl.According to the present invention, the term “the nitrogen-containingheterocyclic group” refers to a non-aromatic 5 to 8-membered monocyclicring having 1 to 3 heteroatoms, a 12-membered bicyclic ring having 1 to6 heteroatoms, or a 11 to 14-membered tricyclic ring having 1 to 9heteroatoms (in which the heteroatoms are nitrogen), examples thereofincluding, but not limited to, pyridyl, imidazolyl, morpholinyl,piperidyl, piperazinyl, pyrrolidinyl, pyrrolidinonyl and the like.Preferably, the each group D is independently:

According to an embodiment of the present invention, m in the polyimideprecursors of formulae (2) to (5) is an integer from 0 to 100,preferably 5 to 50, more preferably 5 to 25; and n in the polyimideprecursor of formula (6) is an integer of higher than 0, preferably aninteger from 1 to 1000.

In the present invention, the precursor composition can further includea solvent, preferably a polar, aprotic solvent. For example, the aproticsolvent can be selected from a group consisting of N-methylpyrrolidone,dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, toluene,xylene, propylene glycol methyl ether (PGME), propylene glycol methylether acetate (PGMEA), γ-butyrolactone (GBL), tetraethylene glycoldimethyl ether (TGDE) and a combination thereof.

The precursor composition according to the present invention mayoptionally include some additives that are known in the art for thepreparation of polyimide, for example, a leveling agent, a defoamingagent, a coupling agent, a dehydrating agent, a catalyst, an opticalinitiator, and etc.

The present invention also provides a method for polymerization of theprecursor composition by low temperature imidization and a polyimideobtained therefrom. The method comprises polymerization of theaforementioned precursor composition by low temperature imidization. Inan embodiment of the present invention, the low temperature imidizationis carried out at a temperature of not higher than 250° C., preferablynot higher than 200° C. For example, the method for preparing polyimidecomprises:

1. Polymerization of Polyimide Precursor

As exemplified by the polyimide precursor of formula (4), thepolymerization scheme includes:

(a) reacting a dianhydride of formula (9) with a compound havinghydroxyl (R—OH) to form a compound of formula (10);

(b) adding a diamine compound of formula H₂N—P—NH₂ to the productobtained from step (a), to form an amic acid ester oligomer of formula(11); and

(c) optionally incorporating a monomer having a photosensitivepolymerizable group (R_(x)), such as epoxy acrylate, for carrying outreaction to form the polyimide precursor of formula (12)

2. Preparation of Polyimide Film

Then, appropriate amounts of an additive and the base generator of thepresent invention are mixed with the polymide precursor of formula (12)and the solution is stirred homogeneously under nitrogen. After that,the resin solution is applied on a copper foil by knife coating and thenbaked in an oven. The baking includes two stages: the first stageinvolving heating from room temperature to 120 to 170° C. in 20 to 50minutes and curing for 30 to 90 minutes at 120 to 170° C., and thesecond stage involving heating up to 200 to 250° C. and curing for 60 to240 minutes at 200 to 250° C. After curing, the copper foil is removedby etching to obtain a polyimide film.

The following examples will exemplify aspects of the present inventionand explain the technical features of the present invention, but are notintended to confine the scope of the present invention. Bothmodification and equivalent arrangement made readily by anyone skilledin the art fall within the scope claimed by the present invention, whichshall be defined by the appended claims.

Example 1 Preparation of Base Generator According to the PresentInvention

Base Generator Compound 1:

Under nitrogen, imidazole was dissolved in anhydrous tetrahydrofuran(THF), and an appropriate amount of di-tert-butyl dicarbonate wasdropped slowly into the solution; then reaction was carried out forabout 2 hours accompanied by effervescent and exothermic phenomena.After the reaction was completed, the solvent and tert-butyl alcoholbyproduct were removed by vacuum reduced pressure concentration toprovide compound 2 as white solid, with yield of about 95%.

Next, under nitrogen, compound 2 was dissolved in dichloromethane, andcompound 3 (trimethyloxonium tetrafluoroborate) was dropped slowly intothe solution at 0° C.; then reaction was carried out for about 2 hoursat room temperature. After that, the solution was added to ether togenerate a solid precipitate; then the solution was filtered and theobtained solid was rinsed with ether to provide compound 1 as whitesolid, with yield of about 70%.

Example 2 Preparation of Base Generator According to the PresentInvention

Base Generator Compound 6:

Under nitrogen, 2-methylimidazole was dissolved in anhydrous THF, and anappropriate amount of di-tert-butyl dicarbonate was dropped slowly intothe solution; then reaction was carried out for about 2 hoursaccompanied by effervescent and exothermic phenomena. After the reactionwas completed, the solvent and tert-butyl alcohol byproduct were removedby vacuum reduce pressure concentration to provide compound 7 as whitesolid, with the yield of about 89%.

Next, under nitrogen, compound 7 was dissolved in dichloromethane, andcompound 3 was dropped slowly into the solution at 0° C.; then reactionwas carried out for about 2 hours at room temperature. After that, thesolution was added to ether to generate a solid precipitate; then thesolution was filtered and the obtained solid was rinsed with diethylether to provide compound 6 as white solid, with yield of about 73%.

Example 3 Preparation of Base Generator According to the PresentInvention

Base Generator Compound 8:

Under nitrogen, 9-fluorenylmethyl chloroformate was dissolved in ether,and an appropriate amount of 1-methyl imidazole was dropped slowly intothe solution under ice bath condition. The solution was stirredcontinuously for about half an hour under ice bath condition, and thenreaction was carried out for about 2 hours at room temperature. Afterthat, the solvent was removed by vacuum reduced pressure concentration;and crystallization was carried out with ethanol for purification toprovide compound 8 as yellow crystalline solid, with yield of about 95%.

Example 4 Preparation of Base Generator According to the PresentInvention

Base Generator Compound 9:

Under nitrogen, benzyl chloroformate was dissolved in ether, and anappropriate amount of 1-methyl imidazole was dropped slowly into thesolution under ice bath condition. The solution was stirred continuouslyfor about half an hour under ice bath, and then reaction was carried outfor about 2 hours at room temperature. After that, the solvent wasremoved by vacuum reduced pressure concentration; and crystallizationwas carried out with ethanol for purification, to provide compound 9 aslight yellow crystalline solid, with yield of about 85%.

Example 5 Preparation of Base Generator According to the PresentInvention

Base Generator Compound 10:

Under nitrogen, imidazole was dissolved in anhydrous THF, and anappropriate amount of acetic anhydride was dropped slowly into thesolution; then reaction was carried out for about half an houraccompanied by exothermic phenomena. After the reaction was completed,the solvent was removed by vacuum reduced pressure concentration togenerate a solid product. Then, the obtained solid was rinsed withn-hexane and filtered to provide compound 11 as white solid, with yieldof about 98%.

Next, under nitrogen, compound 11 was dissolved in dichloromethane, andcompound 3 was dropped slowly into the solution at 0° C.; then reactionwas carried out for about 2 hours at room temperature. After that, thesolution was added to ether to generate a solid precipitate, and thesolution was filtered and the obtained solid was rinsed with ether toprovide compound 10 as white solid, with yield of about 81%.

Example 6 Preparation of Polyimide Film with the Base GeneratorAccording to the Present Invention

(a) Preparation of Polyimide Precursor

Polyimide precursor 4: 29.42 g (0.1 mole)3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) was dissolved in200 g NMP, and the solution was heated to 50° C. and stirred for 2 hoursfor reaction. Then, 13.01 g (0.01 mole) 2-hydroxyethyl methacrylate(HEMA) was dropped slowly into the solution and stirred at a fixedtemperature of 50° C. for reaction for 2 hours. After reaction, 10.814 g(0.1 mole) p-phenylenediamine (pPDA) was added to the solution, andafter complete dissolution, the solution was stirred at a fixedtemperature of 50° C. for reaction for 6 hours to provide the polyimideprecursor 4.

(b) Preparation of Polyimide Film

100 parts by weight of the polyimide precursor 4 and 1 part by weight ofthe base generator compound 1 obtained from Example 1 were mixedhomogeneously under nitrogen. The mixture was applied uniformly on acopper foil by knife coating and then baked in an oven. The bakingincludes two stages: the first stage involving heating from roomtemperature to 150° C. in 35 minutes and curing for 30 minutes at 150°C., and the second stage involving heating from 150° C. to 200° C. andcuring for 120 minutes at 200° C. (the final curing temperature of 200°C. can be changed to 250° C., 300° C. or higher, and the heating ratescan all be 3.5° C./minute). After curing, the copper foil was removed byetching to provide the polyimide film.

Example 7 Preparation of Polyimide Film with the Base GeneratorAccording to the Present Invention

(a) Preparation of Polyimide Precursor

Polyimide precursor 5: 29.42 g (0.1 mole) BPDA was dissolved in about880 g NMP, and the solution was heated to 50° C. and stirred for 2 hoursfor reaction. Then, 3.71 g (0.05 mole) n-butanol was dropped slowly intothe solution and stirred for 4 hours at a fixed temperature of 50° C.for reaction. After reaction, 30.01 g (0.15 mole) 4,4′-oxydianiline(ODA) was added to the solution at room temperature, and after completedissolution, 37.85 g (0.35 mole) pPDA was added to the solution, andafter complete dissolution, 117.68 g (0.4 mole) BPDA was added to thesolution. Then, the solution was stirred at a fixed temperature of 50°C. for 8 hours for reaction to provide the polyimide precursor 5.

(b) Preparation of Polyimide Film

After 100 parts by weight of the polyimide precursor 5 and 1 part byweight of the base generator compound 1 obtained from Example 1 weremixed homogeneously under nitrogen, the same method as that in Example6(b) was used to prepare a polyimide film.

Example 8 Preparation of Polyimide Film with the Base GeneratorAccording to the Present Invention

After 100 parts by weight of the polyimide precursor 4 obtained fromExample 6 and 1 part by weight of the base generator compound 6 obtainedfrom Example 2 were mixed homogeneously under nitrogen, the same methodas that in Example 6(b) was used to prepare a polyimide film.

Example 9 Preparation of Polyimide Film with the Base GeneratorAccording to the Present Invention

After 100 parts by weight of the polyimide precursor 5 obtained fromExample 7 and 1 part by weight of the base generator compound 6 obtainedfrom Example 2 were mixed homogeneously under nitrogen, the same methodas that in Example 6(b) was used to prepare a polyimide film.

Example 10 Preparation of Polyimide Film with the Base GeneratorAccording to the Present Invention

After 100 parts by weight of the polyimide precursor 4 obtained fromExample 6 and 1 part by weight of the base generator compound 8 obtainedfrom Example 3 were mixed homogeneously under nitrogen, the same methodas that in Example 6(b) was used to prepare a polyimide film.

Example 11 Preparation of Polyimide Film with the Base GeneratorAccording to the Present Invention

After 100 parts by weight of the polyimide precursor 5 obtained fromExample 7 and 1 part by weight of the base generator compound 8 obtainedfrom Example 3 were mixed homogeneously under nitrogen, the same methodas that in Example 6(b) was used to prepare a polyimide film.

Example 12 Preparation of Polyimide Film with the Base GeneratorAccording to the Present Invention

After 100 parts by weight of the polyimide precursor 4 obtained fromExample 6 and 1 part by weight of the base generator compound 9 obtainedfrom Example 4 were mixed homogeneously under nitrogen, the same methodas that in Example 6(b) was used to prepare a polyimide film.

Example 13 Preparation of Polyimide Film with the Base GeneratorAccording to the Present Invention

After 100 parts by weight of the polyimide precursor 5 obtained fromExample 7 and 1 part by weight of the base generator compound 9 obtainedfrom Example 4 were mixed homogeneously under nitrogen, the same methodas that in Example 6(b) was used to prepare a polyimide film.

Comparative Example 1 Preparation of Polyimide with Conventional BaseGenerator

Conventional Base Generator 12:

According to a synthetic method (Mitsuru Ueda, Chemistry Letters, 2005,Vol. 34, p. 1372-1373), 2,6-dimethyl-piperidine, di-tert-butyldicarbonate and 4-(dimethylamino)pyridine (DMAP) were mixed together andheated at a temperature of 50° C. for 12 hours, and then the mixture waswashed with water and extracted prior to reduced pressure distillation,to provide a colorless liquid, with yield of about 59%.

Next, 1 part by weight of conventional base generator compound 12 and100 parts by weight of the polyimide precursor 4 obtained from Example 6were mixed homogeneously under nitrogen, and the same method as that inExample 6(b) was used to prepare a polyimide film.

Comparative Example 2 Preparation of Polyimide with Conventional BaseGenerator

After 100 parts by weight of the polyimide precursor 5 obtained fromExample 7 and 1 part by weight of the conventional base generatorcompound 12 were mixed homogeneously under nitrogen, the same method asthat in Example 6(b) was used to prepare a polyimide film.

Comparative Example 3 Preparation of Polyimide without Base Generator

The polyimide precursor 4 obtained from Example 6 was applied onto acopper foil by direct knife coating, and then the same method as that inExample 6(b) was used to prepare a polyimide film.

Comparative Example 4 Preparation of Polyimide without Base Generator

The polyimide precursor 5 obtained from Example 7 was applied onto acopper foil by direct knife coating, and then the same method as that inExample 6(b) was used to prepare a polyimide film.

Physical Property Testing of Polyimide Films

FIG. 1 shows a flow chart for physical property testing of polyimidefilms according to the present invention. Table 1 shows the propertiesof the polyimide films prepared from the polyimide precursor 4 obtainedfrom Example 6.

TABLE 1 Final curing T_(g) ⁽¹⁾ CTE⁽²⁾ Td_(5%) ⁽³⁾ Polyimide filmstemperature (° C.) (° C.) (ppm) (° C.) Example 6 200 362.55 2.77 425.40250 364.29 1.51 589.45 300 365.68 1.05 598.20 Example 8 200 350.42 3.53427.40 250 364.33 2.18 590.87 300 365.15 1.49 599.71 Example 10 200353.18 4.44 399.70 250 364.80 2.15 575.15 300 366.14 1.17 587.58 Example12 200 360.43 2.13 407.15 250 366.81 1.09 553.21 300 366.88 0.98 561.18Comparative 200 345.15 3.24 352.46 Example 1 250 353.44 5.93 560.33 300361.33 3.22 599.33 Comparative 200 205.25 6.31 330.45 Example 3 250208.40 2.20 541.71 300 301.82 2.95 540.30 350 352.90 1.89 539.25  350⁽⁴⁾ 364.18 0.79 537.79 ⁽¹⁾Glass transition temperature⁽²⁾Coefficient of thermal expansion ⁽³⁾Pyrolytic temperature for 5%weight loss ⁽⁴⁾Heating profile: heating from room temperature to 150° C.in 20 minutes, maintaining 150° C. for 120 minutes; then heating to 250°C. in 20 minutes, and maintaining 250° C. for 60 minutes (at a heatingrate of 3.5° C./minute); then heating to 350° C. in 50 minutes andmaintaining this temperature for 120 minutes.

Table 2 shows the properties of the polyimide films prepared from thepolyimide precursor 5 obtained from Example 7.

TABLE 2 Final curing T_(g) ⁽¹⁾ CTE⁽²⁾ Td_(5%) ⁽³⁾ Polyamide filmstemperature (° C.) (° C.) (ppm) (° C.) Example 7 200 330.91 16.41 435.13250 341.14 11.31 586.49 300 343.14 9.62 587.60 Example 9 200 318.5116.38 430.00 250 337.15 13.11 580.30 300 340.55 11.52 579.13 Example 11200 324.15 15.99 418.18 250 339.00 12.00 579.80 300 343.29 10.11 584.54Example 13 200 333.23 15.73 420.83 250 344.18 11.19 543.15 300 343.5711.00 569.18 Comparative 200 313.43 18.15 358.15 Example 2 250 334.7713.17 565.61 300 340.67 11.38 577.33 Comparative 200 221.25 19.58 418.79Example 4 250 280.68 16.42 579.97 300 307.49 12.87 565.30 350 337.7510.26 570.13   350⁽⁴⁾ 340.15 10.15 580.29 ⁽¹⁾Glass transitiontemperature ⁽²⁾Coefficient of thermal expansion ⁽³⁾Pyrolytic temperaturefor 5% weight loss ⁽⁴⁾Heating profile: heating from room temperature to150° C. in 20 minutes, maintaining 150° C. for 120 minutes; then heatingto 250° C. in 20 minutes, and maintaining 250° C. for 60 minutes (at aheating rate of 3.5° C./minute); then heating to 350° C. in 50 minutesand maintaining this temperature for 120 minutes.

The glass transition temperature and the coefficient of thermalexpansion were measured by thermo-mechanical analyzer TA TMA Q-400. Thecoefficient of thermal expansion of the polyimide film was measured at aheating rate of 10° C./minute at from 40 to 300° C. in nitrogenaccording to ASTM-D3386.

The temperature for 5% weight loss of the polyimide film relative to theinitial weight of the polyimide film was employed as the pyrolysistemperature Td_(5%). The pyrolysis temperature for 5% weight loss(Td_(5%)) was measured by thermogravimetric analyzer TA Q-5000 at aheating rate of 20° C./minute from 30 to 900° C.

Films Prepared from Polyimide Precursor 4

It can be seen from Table 1 that the polyimide films prepared from thepolyimide precursor composition according to the present inventionexhibit excellent thermal and mechanical properties even when they werecured at low temperature of 200° C., and have higher glass transitiontemperatures than those of Comparative Example 3 (the polyimide filmwithout addition of a base generator) and Comparative Example 1,demonstrating that the present invention can effectively promotecyclization of polyamic acid. In addition, most of the films obtainedfrom the examples of the present invention have a lower coefficient ofthermal expansion than that of the films obtained from the comparativeexamples.

In Comparative Example 3 (polyimide film without addition of a basegenerator), the glass transition temperature was raised higher than 350°C. only if the curing temperature was higher than 350° C.; and the glasstransition temperature was raised higher than 360° C. only if theheating profile was changed (see the final curing temperature 350° C. inTable 1). Nevertheless, the glass transition temperatures of thepolyimide films obtained from the polyimide precursor 4 of the presentinvention were raised to 360° C. only with the curing temperature of250° C.

It can be seen from the data from the thermogravimetric analyzer that,due to addition of the base generator of the present invention, thecyclization rate of polyimide was increased and the pyrolytictemperature for 5% weight loss was also raised.

Films Prepared from Polyimide Precursor 5

It can be seen from Table 2 that the physical properties of the filmsprepared from polyimide precursor 5 were similar to those from polyimideprecursor 4. From this, it can be concluded that the base generatorsaccording to the present invention are useful for various types ofpolyimide precursors.

Given the above, compared to conventional polyimide films, the polyimidefilms prepared from the precursor composition comprising the polyimideprecursor and the base generator precursor of the present invention bycuring at a low temperature have a higher rate of cyclization than thatof the comparative examples, and are advantageous in terms of glasstransition temperature, coefficient of thermal expansion and pyrolytictemperature for 5% weight loss, thus enabling use in a wide range ofapplications.

What is claimed is:
 1. A base generator having the structure of formula(1):

wherein R₁ is H, linear or branched C₁-C₆ alkyl, linear or branchedC₁-C₆ haloalkyl, linear or branched C₁-C₆ alkyl substituted with one ormore C₆-C₁₄ aryl,

and R₂ is

wherein R₆ is branched C₁-C₆ alkyl, linear or branched C₁-C₆ haloalkyl,linear or branched C₁-C₈ alkoxy unsubstituted or substituted with one ormore C₆-C₁₄ aryl, or —NR₁₀R₁₁, and R₇, R₈, R₁₀ and R₁₁ are the same ordifferent, and are each independently H, linear or branched C₁-C₁₄ alkylunsubstituted or substituted with one or more C₆-C₁₄ aryl, or C₆-C₁₄aryl, and R₉ is H, linear or branched C₁-C₁₄ alkyl substituted with oneor more C₆-C₁₄ aryl, or C₆-C₁₄ aryl; R₃, R₄ and R₅ are the same ordifferent, and are each independently H, linear or branched C₁-C₆ alkylunsubstituted or substituted with one or more C₆-C₁₄ aryl, linear orbranched C₁-C₆ hydroxyalkyl, linear or branched C₁-C₆ cyanoalkyl, orC₆-C₁₄ aryl; and Y^({circle around (−)}) is an anionic group.
 2. Thebase generator according to claim 1, wherein R₁ is linear or branchedC₁-C₆ alkyl,

and R₂ is

wherein R₆ is branched C₁-C₆ alkyl, linear or branched C₁-C₆ haloalkyl,linear or branched C₁-C₈ alkoxy unsubstituted or substituted with one ormore C₆-C₁₄ aryl, or —NR₁₀R₁₁; and R₇, R₈, R₁₀ and R₁₁ are the same ordifferent and are each independently H, linear or branched C₁-C₁₄ alkylunsubstituted or substituted with one or more C₆-C₁₄ aryl, or C₆-C₁₄aryl; and R₉ is H, linear or branched C₁-C₁₄ alkyl substituted with oneor more C₆-C₁₄ aryl, or C₆-C₁₄ aryl.
 3. The base generator according toclaim 1, wherein R₁ is methyl, ethyl, propyl, butyl or selected from agroup consisting of:

and R₂ is


4. The base generator according to claim 1, wherein R₁ is methyl, ethylor selected from a group consisting of:


5. The base generator according to claim 1, wherein R₃, R₄ and R₅ arethe same or different and are each independently H, methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl,hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, hydroxypentyl,hydroxyhexyl, cyanomethyl, cyanoethyl, cyanopropyl, cyanobutyl,cyanopentyl, cyanohexyl, phenyl, benzyl or diphenylmethyl.
 6. The basegenerator according to claim 1, wherein R₃, R₄ and R₅ are the same ordifferent and are each independently H, methyl, ethyl, n-propyl orisopropyl.
 7. The base generator according to claim 1, wherein theanionic group is selected from a group consisting of halide ion,sulfate, nitrate, phosphate, sulfonate, carbonate, tetrafluoborate,borate, chlorate, iodate, hexafluorophosphate, perchlorate,trifluoromethanesulfonate, trifluoroacetate, acetate,tert-butylcarbonate, (CF₃SO₂)₂N⁻ and tert-butyloxy.
 8. The basegenerator according to claim 1, wherein the anionic group is a halideion or tetrafluoroborate.
 9. The base generator according to claim 1,which is an optical base generator or a thermal base generator.
 10. Abase generator having the structure of formula (1):

wherein R₁ is H, or linear or branched C₁-C₆ haloalkyl, and R₂ is linearor branched C₁-C₆ alkyl substituted with one or more C₆-C₁₄ aryl,

wherein R₇ and R₈ are the same or different, and are each independentlyH, linear or branched C₁-C₁₄ alkyl unsubstituted or substituted with oneor more C₆-C₁₄ aryl, or C₆-C₁₄ aryl, and R₉ is H, linear or branchedC₁-C₁₄ alkyl substituted with one or more C₆-C₁₄ aryl, or C₆-C₁₄ aryl;R₃, R₄ and R₅ are the same or different, and are each independently H,linear or branched C₁-C₆ alkyl unsubstituted or substituted with one ormore C₆-C₁₄ aryl, linear or branched C₁-C₆ hydroxyalkyl, linear orbranched C₁-C₆ cyanoalkyl, or C₆-C₁₄ aryl; and Y^({circle around (−)})is an anionic group.
 11. The base generator according to claim 1,wherein R₁ is linear or branched C₁-C₆ alkyl.
 12. The base generatoraccording to claim 10, wherein R₁ is linear or branched C₁-C₆ haloalkyl.13. The base generator according to claim 1, wherein R₁ is linear orbranched C₁-C₆ alkyl substituted with one or more C₆-C₁₄ aryl,